This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-055103, filed Feb. 28, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an iron component used in a built-in disc drive of a personal computer or the like and a manufacturing method therefor.
2. Description of the Related Art
A hard disc drive (HDD) that is used in information processing equipment, such as a personal computer, comprises a disc that is rotated by means of a motor and a carriage that is provided with a head portion for recording in and reading data from the disc. The carriage is turned around a shaft by means of a positioning motor. The carriage includes an actuator arm, a suspension attached to the distal end portion of the actuator arm, the head portion provided on the distal end portion of the suspension, etc. The head portion is provided with a slider.
When the slider is slightly lifted above the surface of the disc as the disc rotates, an air bearing is formed between the disc surface and the slider. The suspension includes a base portion having a base plate, a load beam formed of a precision leaf spring, a flexure fixed to the load beam, and the like. The base plate (mount plate), which is formed of a ferrous metal such as austenitic stainless steel, is formed in a given shape by pressing.
In some cases, burrs may be formed on the shear surface of a component (e.g., base plate) that is formed by machining such as pressing. Since these burrs lower the flatness of the component or fall off, thereby producing particles, they should be removed. Barrel finishing is a known polishing method for removing the burrs. For the barrel finishing, a large number of components, objects to be polished, are stored together with abrasive grains called media in a polishing tank.
The surface of each object is polished by means of the abrasive grains as the polishing tank is rotated. Various known materials are used for the abrasive grains depending on the purposes. Rigid abrasive grains formed of alumina, silicone, or other oxides can be effectively used to remove burrs on stainless-steel components such as the base plate.
The oxide-based abrasive grains are rigid enough to remove the burrs effectively. On the other hand, minute fragments of the abrasive grains are supposed to be stuck in the surface of each component. Possibly, the fragments of the abrasive grains in the surface of the component may remain in the component surface, failing to be removed by cleaning that follows polishing, and form contaminants. If minute fragments (or particles) of the abrasive grains of several micrometers fall from the surface of the base plate during use of a disc drive (or operation of a computer), the particles may possibly get into the space between the disc and the slider. These particles may exert a bad influence upon the performance of the disc drive.
In order to prevent the particles from falling off (or from producing contaminants), the possibility of contaminants production may be lowered by thoroughly cleaning the polished component by ultrasonic cleaning or the like, thereby removing as many particles that can fall off as possible. However, even the thoroughgoing ultrasonic cleaning cannot entirely remove the particles that are stuck in the surface of the component. Alternatively, the particles in the component surface may be removed by chemical polishing. Essentially, however, the chemical polishing is a process in which the whole surface of a component is melted down. Thus, the chemically polished component is subject to variation in dimensions, and the addition of the process results in an increase in cost.
The object of the present invention is to provide a high-cleanness iron component restrained from producing dust and a manufacturing method therefor.
An iron component according to the present invention comprises an iron body material formed having a given shape and polished, an oxide in the constituents of fragments of an oxide abrasive material in and near the surface of the body material being reduced so that iron is dispersed into the body material. According to this invention, production of dust after polishing can be restrained, so that the iron component obtained is highly clean. In this specification, xe2x80x9ciron componentxe2x80x9d is a stainless-steel component that is used in a disc drive, for example.
More specifically, an example of the iron component is a component for disc drive, such as a base plate of a suspension for disc drive formed of austenitic stainless steel or a dummy head (dummy component equivalent to a suspension in mass). In a disc drive in which production of particles in a casing must be minimized, according to this invention, particles can be restrained from falling from the stainless-steel component into the casing, so that the interior of the disc drive can be kept highly clean. However, the invention is applicable to any other precision components than the disc drive that require high cleanness. In this specification, xe2x80x9cironxe2x80x9d is a steel material that contains 50% or more of Fe (iron element). Further, xe2x80x9creductionxe2x80x9d results in a state in which equivalence of the oxygen concentration to that of the body material can be recognized by surface characterization such as EDX. xe2x80x9cReducing atmospherexe2x80x9d is a concept that covers a vacuum.
A manufacturing method for an iron component according to the present invention comprises a polishing process of polishing the surface of an iron body material having a given shape by means of an abrasive material containing ferric oxide, and a heat treatment process of heating the body material in a reducing atmosphere after the polishing process, thereby reducing an oxide in the constituents of fragments of the abrasive material in and near the surface of the body material and leaving iron, and keeping the body material at a temperature for dispersion, thereby dispersing the iron into the body material. The temperature for the heat treatment ranges from 300xc2x0 C. to 1,540xc2x0 C. In the case of stainless steel, in particular, the suitable heat treatment temperature ranges from 800xc2x0 C. to 1,100xc2x0 C.
According to the manufacturing method of this invention, burrs on the iron component can be effectively removed by means of the oxide abrasive material, and the fragments of the abrasive material and fragments of the body material can be extinguished by heat treatment for dispersion that is carried out in the reducing atmosphere after the polishing. Thus, the iron component obtained is highly clean.
The conditions in which the fragments of the abrasive material formed of ferric oxide can be extinguished by the heat treatment depend on the reducing atmosphere of hydrogen and the heat treatment temperature. Hydrogen has reducibility such that it can maintain the surface of a ferrous metal without oxidizing or exerting any influence upon the metal and reduce oxides. Accordingly, the fragments of the abrasive material formed of ferric oxide that are adhered to or stuck in the surface of the iron body material are reduced to Fe in the reducing atmosphere, and the resulting Fe is dispersed into the iron body material (e.g., austenitic stainless steel). Thereupon, the fragments of the abrasive material in the surface of the iron body material disappear.
The heat treatment process according to the present invention serves highly effectively to restrain production of particles from the component of austenitic stainless steel. However, it also serves to restrain production of particles from iron components of various other steel materials including martensitic stainless steel, ferritic stainless steel, etc. Further, the present invention is applicable to any other iron components than the disc drive, not to mention dummy heads or other iron components that are incorporated in disc drives as well as base plates of suspensions for disc drive.
The polishing process according to the invention may be any other processes than barrel finishing, such as ones based on shot blasting or a lapping machine. In short, the polishing process is a process using an abrasive material that consists mainly of ferric oxide. If any of minute fragments of the abrasive material or fragments of the body material that are produced by the polishing may possibly be adhered to or stuck in the body material, the aforesaid process of heat treatment in the reducing atmosphere serves very effectively to restrain production of particles or dust.
According to the present invention, the iron component that is restrained from producing dust by the heat treatment in the reducing atmosphere is incorporated in the casing of a hard disc drive or the like in which production of dust in the casing must be minimized. Thus, the reliability of the hard disc drive or other device can be improved effectively.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.